The present invention relates generally to prosthesis and instruments used during knee surgery for the reinstatement of the natural knee joint. More particularly, the invention relates to a unicondylar femoral prosthesis and the instruments used to properly size and locate the prosthesis using anterior or posterior referencing.
For various reasons, the human knee fails at the tibial and femoral juncture causing great pain and suffering to the individual. To correct this problem, surgeons now replace all or part of the natural knee joint with artificial components. In one type of partial knee replacement, an artificial tibial component is placed on the proximal end of the tibia and an artificial femoral component is placed on the distal end of the femur.
Because each individual""s femur and tibia are different in size and because the extent of damage to the tibia and femur ends cannot accurately be determined until after the knee has been opened by the surgeon, the size of the implant components cannot be easily determined prior to the operation. Accordingly, it is common practice to initiate the operation, open up the knee, fully evaluate the needs of the patient and, at that time, determine the size of the femoral and tibial components required. In view of this practice, manufacturers of femoral and tibial components typically manufacture five to eight different size component sets to be available to the surgeon during the operation.
Additionally, once the knee is open, the surgeon evaluates the patient to determine which of two referencing methods will best suit the patient. In anterior referencing, careful attention is given to the patellofemoral joint by using an anteriorally placed feeler gage. This referencing system focuses on allowing proper ligament balance and stability in extension as well as consistent patellofemoral placement on the anterior surface.
A second type of instrument design (posterior referencing) is based on the concept that flexion and extension stability are more important than the patello transition location. Specifically, the flexion gap is better balanced to avoid laxity in flexion or tightness in flexion.
In the case of sizing the femoral distal end in determining which of the femoral component sizes to use, the common practice has been to measure the anterior to posterior distance of the femur and, utilizing this measurement, to pick an appropriate size femoral component. Unfortunately, this technique is relatively invasive because the instrument used to measure the anterior to posterior femoral distal end distance is relatively large and unwieldy.
Many surgeons wishing to avoid patient morbidity associated with the aforementioned invasive procedure have chosen an instrument free method of resection. In this method, the surgeon removes portions of the femoral distal end with a burr operated by hand without the use of a resection guide. While such a method is less invasive, the resected surface created by the burr is not accurately located relative to a reference point. Unfortunately, variation in the final positioning of the femoral component occurs.
Accordingly, an object of the present invention is to provide a method and apparatus enabling implantation of a unicondylar femoral prosthesis with minimal bone removal.
Another object of the present invention is to provide a minimally invasive technique for producing reproducible bone resections using either anterior or posterior referencing.
The present invention relates to a set of femoral orthopedic devices and a method of implanting the devices. The set of femoral orthopedic devices includes a first component having a first size and a second component having a second size. The first component includes a peg positioned a predetermined distance from a first reference point The second component includes a peg positioned a predetermined distance from said first reference point. The method calls for referencing a femoral condyle at a first reference point, locating a peg aperture a predetermined distance from the first reference point, selecting a sized femoral component, and implanting the femoral component. The size of the femoral component is defined by a distance from the peg to a second reference point.